Bond strength of steel rebar and concrete after different cooling methods: Experimental study and theoretical modeling

Water spray cooling is a commonly used method to cool structures after fire exposure. However, existing studies have largely overlooked the impact of factors such as cooling methods, concrete cover thickness, and stirrup ratio on the bond failure mode between steel rebar and concrete, and have rarely examined the bond failure mechanism in detail. To address these issues, this study conducted pull-out tests on 126 specimens, considering the influence of various parameters. The failure modes and bond slip responses under different conditions were recorded and analyzed, leading to the establishment of preliminary criteria for identifying bond failure modes. Digital Image Correlation (DIC) was employed to monitor the strain field during and after cooling, providing insights into the dynamic evolution of cracks in the concrete. An improved bond strength prediction model was developed to account for different failure modes, incorporating the interaction between longitudinal-radial and radial-circumferential stress planes. The model enables comprehensive prediction, from test input parameters to failure mode identification and bond strength evaluation. This method provides a more accurate mechanical basis for assessing bond deterioration after fire exposure. It also offers practical guidance for repairing fire-damaged concrete structures.